1. Field of the Invention
The present invention pertains to methods and apparatus for separating a volatile constituent from a liquid mixture, and more particularly, it pertains to methods and apparatus for steam stripping liquid mixtures in a continuous operation in order to extract a volatile constituent thereof.
2. Description of the Prior Art
Steam distillation, or steam stripping, is a well known process in which vaporization of the volatile constituents of a charge of liquid material is effected at a lowered temperature by the introduction of steam directly into the charge. Steam stripping is normally used where the constituents to be separated are not sufficiently volatile to vaporize under normal controlled heating conditions. Typical steam stripping installations of the prior art include the vertically arranged packed columns or plate columns wherein the liquid feed material is inserted under equilibrium conditions into the column where countercurrent flow provides a continuous separation of the vapor and liquid phases of the material. The columns normally contain a plurality of rings, plates, or other forms of baffles so as to provide a maximum number of turbulence producing and mixing surfaces. Steam is bubbled up from the bottom of the tank to provide a thorough mixing and vapor-stripping of the material in the column, and the vapors are removed at the top of the column while the spent liquor is continuously drained off at the bottom of the column. A duel-stage steam stripping apparatus for recovering vegetable oils from an oil and solvent solution of hot miscella is shown, for example, in prior U.S. Pat. No. 3,503,854 to Good.
The aforementioned steam stripping apparatus and processes of the prior art, however, are not always ideally efficient where the material to be separated comprises an emulsion and, particularly, where the volatile constituent may be entrained in fine particulate matter in the emulsion. A typical example of an emulsion which cannot be readily separated with normal steam stripping apparatus without long exposure times and the additions of excessive amounts of steam is a citrus peel oil emulsion as obtained from a citrus juice extractor of the type shown, for example, in the prior U.S. Pat. No. 3,717,084 to Robbins et al. In the juice extracting machine shown in this patent, the juice is extracted from citrus fruit, such as oranges, by compressing the fruit between a pair of cups formed with a plurality of interdigitating fingers. One of the cups is provided with a central tube to receive the juice while the peel is scored and pushed through the fingers with the peel oil being discharged therefrom in the process. Washing sprays are used to wash the oil from the peel and from the air, and the resulting peel oil emulsion is directed away from the juice extracting machine.
The major constituent of the essential oil present in citrus fruit peels is known as d-limonene and is useful in making dipentene resins such as turpentine. Approximately 95% of the essential oil in oranges, for example, is d-limonene. With the juice extractor of the aforementioned United States patent to Robbins et al, a water-peel oil emulsion is produced containing about 3-5% by volume of d-limonene with the d-limonene being immiscible in the water. In addition to the d-limonene, the emulsion also contains some coluble solids, mostly sugars and pectins, and insoluble solids in the form of fine pulp particles or bits of peel.
Methods of recovering the d-limonene from the peel oil emulsion have included centrifuging, but the amount of d-limonene recoverable by this type of process is limited. Other prior art suggested methods for recovering the essential oils from the citrus peel oil emulsion have included various more or less conventional steam stripping operations as disclosed, for example, in the U.S. Pat. No. 2,471,893 to Pulley or the article by Messrs. Veldhuis et al in the Journal of Food Science, Volume 37, pages 108-112 (1972). In the patented steam stripping system citrus waste press water is heated to some 215.degree. F. to 250.degree. F., or higher, and is then passed through a holding chamber under sufficient pressure so as to prevent boiling with the retention time of the material in the chamber being about 10 seconds. The press water is flash discharged from the holding chamber into a flash tank through a spray nozzle. In the flash tank steam is introduced into the emulsion with the vapors being collected, condensed and directed to a decant tank where the essential citrus oil is separated from the water. In the process disclosed in the Veldhuis et al article, citrus waste water is directed into a conventional steam stripping column and the vapors therefrom are directed into a reflux condenser and a chilling condenser with the condensate therefrom being delivered to an oil separator.
Other prior art steam stripping processes which have been performed upon fruit juices for recovering volatile constituents thereof are disclosed in an article by A. H. Brown et al in Industrial & Engineering Chemistry, Volume 43, No. 12 (1951). In a process disclosed in this article, the fruit juice material is heated and fed to a steam injection heater. The resultant steam-liquid mixture is then directed to a six-foot, steam-jacketed tubular evaporator before being flashed into a flash tank where the vapor is separated from the liquid, condensed and separated in the conventional manner.